The present invention relates to an impedance coupling device and more particularly to an antenna coupler for use in matching an antenna to a high power transmission line so to enable a high power signal to be radiated with maximum efficiency.
It is well known that an antenna must be tuned or matched to its transmission line for the frequency of the signal being radiated for the purpose of achieving maximum efficiency. At low and medium signal powers, such tuning or matching presents no serious problems. Such coupling can be achieved in a variety of ways, for example, by adjusting capacitor values and by the use of tuning coils. Electronic circuitry is also available for detecting circuit conditions and automatically adjusting the coupling device so as to produce the most effective matching of the antenna with the transmission line for the particular signal under any given conditions.
It should, of course, by borne in mind that the matching of an antenna with its feed line may require different adjustments, depending upon weather conditions and the surrounding conditions of the earth as well as when the signal frequency is varied.
At higher signal powers, however, the effecting of the necessary adjustments to produce efficient antenna coupling presents a more serious problem. For example, with signal frequencies of 1.6 to 30 MHZ at powers in excess of 1 KW, matching has, generally speaking, been effected by manually connecting and disconnecting various components. Such various components are often mounted permanently in position and provided with terminals to facilitate their connection and disconnection. This known procedure, however, requires relatively complicated equipment and also involves serious interruptions in transmission, when the equipment is being adjusted for different signal frequencies.
It can also involve a serious health hazard if the power is not totally interrupted while the adjustments are made.
In addition to being slow and cumbersome, this known system presents the further disadvantage that errors may occur in connecting the terminals of the various components with the result that the matching of the antenna for a new signal might not be achieved.
The use of conventional electrical relays for effecting such connection and disconnection of components is not possible in the presence of the high power electromagnetic fields surrounding such equipment. Additionally, any attempt to isolate conventional relays from such fields, for example, by locating them at a distance from the equipment is impractical since then the length of the electrical conductors between the coupler and such relays would then alter the performance of the coupler. Accordingly, while the problems surrounding the use of manually changeable terminals are quite obvious and have been apparent for many years, no completely satisfactory solution to the problem has heretofore been found.